Light therapy of this type is for instance used for the treatment of affective disorders or circadian rhythm sleep disorders. Timed bright light therapy is the recommended treatment for Circadian Rhythm Sleep Disorders, especially for Shift Work Disorder and Delayed Sleep Phase Disorder; in this respect, reference can be made to the article “Practice Parameters for the Clinical Evaluation and Treatment of Circadian Rhythm Sleep Disorders” from the American Academy of Sleep Medicine in Sleep, Vol. 30, No. 11, 2007. Such therapy involves exposing patients at properly determined times to white light intensities of typically 2500-10,000 lux for periods ranging from 30 minutes to 2 hours. The most commonly used devices are small light boxes that have to be put on a table in front of the user. More recent light therapy devices make use of only the blue part of the light spectrum, because the shifting effect of the human circadian pacemaker system is most sensitive to blue light.
WO-2010/076708 discloses a device that comprises a head-mounted device in the shape of a mask: in such a case, the relative orientation and distance between the device and the user's eyes are always fixed.